I realized that as soon as the phone returned home and re-connected to WiFi, there were no cached entries on the Tracker map. Further investigation showed that there were zero cached entries on the phone as well.

Testing:
1. Turned off Screen Lock (no security)
2. Set screen Timeout to maximum of 10 minutes.
3. Set Hot GPS to on to ensure frequent GPS trackings.
4. Turned off any and all Power Save features on phone.
5. Ensured AT App is active and in foreground (not closed or "clicked the back button" on phone)

Testing conditions:
1. Samsung Galaxy S4- no cell service, no SIM card. WiFi/GPS only.
2. Device placed in car out in the open and tests successfully.
3. All security and power saving functions disabled.
4. AT APP is left open and running at all times.
5. Smart Sending turned off.
6. Hot GPS turned on for fast rates/testing purposes.

Testing observations:
1. While screen is lit up, AT pings out for GPS coords. - SUCCESS
2. Cell is not enabled, therefore no connection can be established, AT caches entry - SUCCESS
3. Being in Hot GPS mode, #2 happens frequently and each attempt is cached - SUCCESS
4. After 10 minutes, I write down the value of cached entries - for example 330.
5. At that time of screen shut-off, AT stops all attempts at GPS tracking and therefore no caching happens - FAILURE
6. I wait another 10 minutes and the quantity of cached tracks equals the amount previously recorded at screen shut-off. - FAILURE
7. I tap any button and the screen lights back up, no security screen, directly to the already (and still) open AT program. The program NEVER shut down.

Summary - Works great if phone never goes into screen dark state. As soon as the screen on the device goes out, all tracking stops and therefore no caching. Once device reconnects to WiFi(car returns home), all previously cached events (previous to car leaving or WiFi being turned off in testing environment) upload to site successfully and then continues to track GPS pings, without having to "open" up phone again! It appears that the logic is as follows (this is not actual code! This is just how my brains sees it!):

IF ScreenTurnedOff = TRUE AND ActiveConnection = TRUE /Screen is lit up and active WiFi connection
THEN ContinueTracking = TRUE
ELSE
IF = ActiveConnection = FALSE AND ScreenTurnedOff = FALSE /This is where the APP still tracks and caches if screen is lit up
THEN ActiveTracking = TRUE
CacheTracks = TRUE
ELSE
IF = ActiveConnection = FALSE AND ScreenTurnedOff = TRUE /This is where the APP stops tracking and caching if screen is dark
THEN ActiveTracking = FALSE /Stops all tracking even if APP is open
CacheTracks = FALSE /Does not cache since active tracking is disabled

Returning home and connects to WiFi WITHOUT touching phone/opening up/making screen light up:

IF = ActiveConnection = FALSE AND ScreenTurnedOff = TRUE /This is where the APP stops tracking and caching if screen is dark
THEN ActiveTracking = FALSE /Stops all tracking even if APP is open
CacheTracks = FALSE /Does not cache since active tracking is disabled
ELSE
UponReconnectionWithWIFI = TRUE AND ScreenTurnedOff = TRUE AND ActiveTracking = FALSE /This is where no "opening" of phone happens and is still in car but App is still running in forground
THEN RestartTracking = TRUE AND DumpCacheToServer = TRUE /if there's any previously cached items in cache from the short time between leaving Wifi area and screen going dark.

Have you tried just put it into background (regardless of screen on or off)?
There's an interesting setup here as well (no SIM card, no cell data network). I wonder that might play a role here as well.